2.0 Analysis 2.1 Introduction During the investigation, it was determined that the aircraft was flown into IMC above the freezing level. It was further determined that the aircraft was flown in areas of high relative humidity, and that the engine lost power during cruise flight. Since the total loss of engine power could not be explained by any observed engine defect, it is therefore necessary to concentrate on the combined effects of the flight preparations, meteorological conditions, and pilot procedures. 2.2 Flight Preparations The hourly weather sequences, forecasts, PIREPs, and satellite photographs indicate that the weather was marginal for a VFR flight via the Tintina Trench route. The en route PIREPs reported the presence of low stratus cloud with precipitation, smoke, and fog obscuring the mountainous terrain. The pilot reported there was no pressure to fly to Watson Lake on the day of the accident. 2.3 Pilot Procedures The pilot flight planned from Dawson direct to Faro, direct to Watson Lake, according to VFR; however, he deviated from this plan by climbing to 11,500 feet asl and flying with reference to flight instruments. He also deviated from his flight plan route by flying an arc off the Whitehorse VOR/DME. Although he was not certified for instrument flight, the pilot had taken about 30 hours of instrument training about eight years prior to the accident; thus he had acquired the basic knowledge to control the aircraft in instrument conditions. Manoeuvring the aircraft in IMC without recent instrument training or certification, during a loss of engine power, would increase the workload for the pilot. The investigation established that the high humidity conditions at the time of take-off, climb to altitude, en route cruise, and descent were conducive to serious carburettor icing. The procedure which was carried out by the pilot when he suspected carburettor ice is contrary to recommended practices. When the pilot selected carburettor heat, it is probable that the hot incoming air melted the carburettor ice that may have accumulated, causing it to enter the cylinders and effect a further loss of engine power. During the descent, the engine continued to lose power until all power was lost. The propeller continued to windmill up until the point of impact. The temperatures aloft for 12,000 feet asl were forecast by AES to be about minus nine degrees Celsius. With a surface temperature of about plus four degrees Celsius, it is likely that the carburettor ice would not have melted during the descent, as the same principles of carburettor ice apply with a windmilling propeller; therefore residual heat from the engine would have been lost during the descent, and surface temperatures would have been cool enough to prolong the melting of the ice. The aircraft is equipped with a carburettor heat and a cabin heat system that share the same exhaust manifold heat source. Rather than being drawn directly into the carburettor, with the application of carburettor heat, the incoming air is circulated around the exhaust stack manifold and heated. However, with the temperatures that were present at cruising altitude, cabin heat would also have been demanded; thus, the output of the carburettor heat supply would have been diminished. The power loss which occurred during cruise flight may, therefore, have been caused by a combination of factors. However, the total loss of power could not be explained by any observed engine defect. The effect of stuck and broken piston rings, fouled spark plugs, and a time-worn engine would be a loss of engine power. In addition, because the aircraft was flown in cloud above the freezing level, it is possible that freezing of fuel vents, impact icing, propeller ice, and carburettor ice may also have contributed to the loss of engine power. The combined effects of these factors would be a loss of power to the extent that continued flight would likely be impossible. 3.0 Conclusions 3.1 Findings The flight was conducted in conditions of atmospheric humidity conducive to serious carburettor icing. The pilot continued visual flight into IMC without being certified for instrument flight. The pilot conducted the flight into a sparsely settled area without the required emergency survival equipment. The pilot conducted the flight at 11,500 feet asl, for more than 30 minutes, without the required oxygen and equipment. The pilot conducted the flight into forecast icing conditions. The aircraft was not certified for flight in icing conditions. There were no entries in the aircraft log-books to indicate that the engine was being maintained On Condition. The pilot deviated from the flight plan route without advising Air Traffic Services of his intentions. Search and Rescue efforts were hampered initially by poor weather conditions, and the lack of an ELT signal. The pilot was not familiar with the operation of the ELT. The ELT was diagnosed as possibly having an intermittent oscillator. The pilot did not declare an emergency following the loss of engine power. Examination of the engine revealed that it was in a time-worn state, and exhibited evidence of stuck and broken piston rings on the No. 3 cylinder which would have contributed to minor loss of engine power. 3.2 Causes The engine power loss was likely due to carburettor icing. Contributing to the accident was the pilot's decision to continue the visual flight into instrument meteorological conditions. The Board has no aviation safety recommendations to issue at this time.4.0 Safety Action The Board has no aviation safety recommendations to issue at this time.